A standard single-lever valve has a deck- or wall-mount housing provided internally with a valve cartridge from which extends an actuating stem. A handle mounted on the stem can pivot about a flow-control axis to adjust the rate of flow through the cartridge and about a different temperature-control axis to control the mix of hot and cold water that is fed to an output, normally a spout. It is therefore possible to adjust flow rate and temperature in an extremely easy manner that the user quickly adjusts to.
Nowadays safety and conservation requirements demand that, however, the valve be capable of limiting the flow rate and/or maximum temperature of the outputted water. Thus abutments are provided as described in European patent applications 0,426,639 of D'Alayer and 0,662,577 of Hirsh as well as in German patent 3,607,349. In these systems it is possible to set the valve so that the maximum temperature it can output is limited and/or the maximum amount of flow through it is limited. In some cases the handle must be actuated with greatly increased force to get past the preset partial-flow or high-temperature setting and in others the handle must be actuated with respect to a third axis in order to override the safety settings.
All such system are fairly cumbersome. In addition the override arrangements are often so complex that with time they either cease functioning altogether so that there is no flow or temperature limit, or so that one cannot override the flow or temperature limit.